1. Field of the Invention
This invention relates to a negative pressure cut valve for use at a site liable to be invaded by water, more particularly to a diaphragm type negative pressure cut valve to be ideally used in a leakproof system for vaporized fuel in an automobile fuel tank.
2. Description of the Prior Art
In the injection of fuel into an automobile fuel tank, the air containing vaporized fuel is apt to leak from the interior of the fuel tank into the ambient air. For the purpose of preventing the leakage of the vaporized fuel into the ambient air, the vapor recovery system such as is disclosed in JP-A-01-126,824, for example, has been developed to date.
This system is adapted to cause the vaporized fuel arising during the injection of fuel to be adsorbed on a canister and, after the engine is started, enable the vaporized fuel in the canister to be effectively utilized for the ensuing operation of the started engine. The adoption of this system, however, requires the capacity of the canister to be larger than usual for the sake of the adsorption of the vaporized fuel.
To ensure the earliest possible consumption of the adsorbed vaporized fuel and enable the canister to resume the function of adsorption for full utilization, the flow volume of the vaporized fuel to be purged from the engine must be increased.
In this case, however, there arises the possibility that the interior of the fuel tank will develop a negative pressure and the fuel tank will succumb to deformation under compression, depending on the flow volume of the vaporized fuel being purged. Means to preclude this possibility, therefore, is needed.
It has been heretofore proposed, therefore, to provide such a diaphragm type negative pressure cut valve 50 as shown in FIG. 9 inside such a vapor recovery system S as shown in FIG. 8, for example.
In FIG. 8, reference numeral 51 stands for a fuel tank, numeral 52 for a filler tube for establishing communication between a fuel inlet and the fuel tank 51, numeral 53 for a canister, numeral 54 for an evaporation shutting valve, numeral 55 for a shutter on the side of the fuel inlet, numeral 56 for a backflow preventing shutter, numeral 57 for a cut valve, numeral 58 for a fuel temperature sensor, numeral 59 for a bypass valve, numeral 60 for a pressure sensor, numeral 61 for a drain cut valve, numeral 62 for a one-way valve, numeral 63 for a duckbill, and numeral 64 for a piping extending from the fuel tank 51 via the evaporation shutting valve 54 to the canister 53.
In FIG. 9, reference numeral 65 stands for a diaphragm, numeral 66 for a compression coil spring, numeral 67 for a flexible umbrellalike valve, numeral 69 for a lower side wall of the cut valve 50 provided with an atmospheric vent 68, numeral 71 for a feed pipe, and numeral 81 for a forward pipe.
The negative pressure cut valve 50, therefore, is arranged in parallel to the bypass valve 59 disposed on the piping 64. The piping 64 has the pressure sensor 60 incorporated therein before it reaches the canister 53.
Now, the operation of the prior art negative pressure cut valve 50 constructed as described above will be explained below. With reference to FIG. 8 and FIG. 9, while the canister 53 is under a reduced pressure, both the diaphragm 65 and the umbrellalike valve 67 retain their shut states to prevent the interior of the fuel tank 51 from assuming negative pressure.
When fuel is injected into the fuel tank 51 and the inner pressure of the fuel tank 51 is consequently increased, the diaphragm 65 assumes its open state to release the pressure toward the canister 53 at the time that the difference of pressure between the feed pipe 71 side and the forward pipe 81 side overcomes the pressure of the compression coil spring 66. When the inner pressure of the fuel tank 51 is conversely lowered, the difference of pressure between the feed pipe 71 side and the forward pipe 81 side sets the umbrellalike valve 67 at its open state to start inflow of the ambient air from the canister 53 side.
For the purpose of enabling the diaphragm 65 to operate smoothly under the conventional negative pressure cut valve 50, therefore, the atmospheric vent 68 must be formed on the operating side of the diaphragm 65, namely on the lower side wall 69 of the cut valve 50 as shown in FIG. 9.
The fact that the atmospheric vent 68 is formed in the lower side wall 69 mentioned above, however, suggests the possibility that the atmospheric vent 68 will admit dirt and other extraneous substances and these intruders will obstruct the operation of the diaphragm 65. It has been, therefore, customary to adopt means to decrease the size of the atmospheric vent 68 to the fullest possible extent. If this decrease is made excessively, however, the vent 68 will operate adversely and cease to ensure smooth operation of the diaphragm 65.
When the vapor recovery system S is mounted on an automobile, it entrains the following problems, depending on the position for laying out the negative pressure cut valve 50.
Since the negative pressure cut valve 50 by nature must be disposed at a position near the fuel tank 51, it is generally installed more often than not in the neighborhood of the rear side. At the position thus selected, it is naturally prone to the influences of water and mud. Particularly when the automobile happens to run into a pool of water on a road, the possibility that the negative pressure cut valve 50 will plung completely in the water is quite fair. If the diaphragm 65 is operated while the negative pressure cut valve 50 remains in the submerged state, the water will find its way through the atmospheric vent 68 and adhere to the diaphragm 65 and compression coil spring 66.
The dirty water deteriorates the diaphragm 65 and compression coil spring 66. If the adhering water freezes, the possibility that the diaphragm 65 itself will no longer be able to operate cannot be denied.
The main object of this invention is to provide a negative pressure cut valve which allows an effective solution of such problems of the prior art as mentioned above and, in particular, permits infallible prevention of the aforementioned adhesion of water and extraneous substances to a diaphragm and a compression coil spring without exerting any adverse effect on the necessary performance of the valve.